<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>id和class选择器</title>
  <style>
    /* id选择器 —— #id名 */
    #div1 {
      background-color: antiquewhite;
    }

    /* 类选择器 —— .class名 */
    .div3 {
      background-color: aqua;
    }
  </style>
</head>

<body>
  <div id="div1">我是div1</div>
  <div id="div2">我是div2</div>
  <div class="div3">我是div3</div>
  <div class="div3">我是div3二号</div>
  <div class="div3 div4">我是多类名div</div>
</body>

</html>